This Fogarty International Research Collaboration award (FIRCA) proposal is on tsetse fly population genetics in order to support the ongoing Human African Trypanosomiasis (HAT) control activities in East Africa. The parent grant (NIAID R01Al068932, 01/01/2008 to 12/31/2012) addresses the molecular and ecological aspects of the two HAT disease belts (gambiense and rhodesiense) in Uganda with a focus on population and evolutionary genetics of tsetse flies and their parasites and endosymbionts. The co- investigator of this FIRCA, Dr. Johnson Ouma, is an experienced tsetse population geneticist who is now the head of tsetse genomic research and Deputy Director of the national Trypanosomiasis Research Center (TRC) in Kenya. Kenya is at risk of HAT outbreaks due to ongoing epidemics in neighboring Uganda and increased movement of people and cattle (known reservoirs for Trypanosoma brucei rhodesiense). Earlier tsetse control efforts in the Lake Victoria basin and in the southern Rift Valley were unsustainable and these regions rapidly became repopulated. It is unknown if the extant G. pallidipes vector populations in Lambwe originated through reinvasion from neighboring populations, or through incomplete elimination of local populations that existed below thresholds of detection. Efforts are underway once again to eliminate G. pallidipes from Lambwe valley and surrounding areas. This application has three aims to: 1) estimate rates of gene flow and degrees of genetic differentiation among G. pallidipes populations around the Lake Victoria basin and in southern Rift Valley, 2) estimate local levels of temporal genetic differentiation and dynamics of G. pallidipes populations from the Lambwe and Nguruman valleys and 3) understand the circulating trypanosome parasite diversity isolated from flies/humans and known reservoir animals in the Lambwe valley. Results will help understand the breeding pattern of G. pallidipes populations in East Africa, and thus identify populations that can serve as potential sources of immigrants into Nguruman and Lambwe. This knowledge is important to the ongoing and planned tsetse control programs and can help develop methods for inclusion or exclusion of adjacent populations to the target population during vector suppression efforts. Knowledge on parasite strains in circulation will also help better understand disease risk and epidemiology.